Physical vapor deposition plasma reactor with arcing suppression

ABSTRACT

A physical vapor deposition reactor includes a vacuum chamber with a sidewall, a ceiling and a retractable wafer support pedestal near a floor of the chamber, and a vacuum pump coupled to the chamber, the retractable wafer support pedestal having an internal electrode and a grounded base with a conductive annular flange extending from the base. A metal sputter target at the ceiling is energized by a high voltage D.C. source. The reactor has an RF plasma source power generator with a frequency suitable for exciting kinetic electrons is coupled to either the sputter target or to the internal electrode of the pedestal. A removable shield protects the sidewall and is grounded by plural compressible conductive tabs dispersed at generally uniform intervals on the annular flange and engaging a bottom edge of the shield whenever the retractable wafer support pedestal is in an unretracted position, each of the uniform intervals being less than a wavelength corresponding to the frequency of the RF plasma source power generator.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.11/052,011 filed Feb. 3, 2005 by Karl M. Brown et al., entitled“APPARATUS FOR METAL PLASMA VAPOR DEPOSITION AND RE-SPUTTER WITH SOURCEAND BIAS POWER FREQUENCIES APPLIED THROUGH THE WORKPIECE” and assignedto the present assignee.

BACKGROUND OF THE INVENTION

With recent technological advances in integrated circuit design, thereare now as many as six to ten interconnect layers of a multilayerinterconnect structure overlying the semiconductor transistors.Insulator layers separate the successive conductor layers. The conductorinterconnect layers can have completely different conductor patterns andare connected to one another and to the transistor layer at differentlocations through vias extending vertically through the insulatorlayers. It is the formation of the vias with which the present inventionis concerned.

To reduce resistive power losses in the integrated circuit, theinterconnect layers and the vias typically employ aluminum and, morerecently, copper as the principal conductor. The insulator layers aresilicon dioxide, although more recently dielectric materials other thansilicon dioxide having a lower dielectric constant are increasinglybeing employed. Because copper tends to diffuse over time through theinsulator layer to cause catastrophic short circuiting, a barrier layerthat blocks copper diffusion is placed between the copper material andthe dielectric material wherever the two materials interface in theintegrated circuit. The barrier layer is typically formed of anunderlying tantalum nitride or titanium nitride layer contacting theinsulator layer, an overlying pure (or nearly pure) tantalum (ortitanium) layer and, finally, a copper seed layer over the pure tantalum(or titanium) layer. If the conductor is to be copper, then tantalum ispreferred. The copper conductor is deposited on the copper seed layer.Such a barrier layer prevents migration or diffusion of copper atomsinto the dielectric material. The tantalum and tantalum nitride (ortitanium and titanium nitride) layers are poor conductors compared tocopper. The formation of the barrier layer and of the copper conductorsis carried out by physical vapor deposition. Other deposition processesmay be employed for the metal fill step (copper deposition) such aschemical vapor deposition, plasma enhanced chemical vapor deposition orelectroplating.

A problem arises in forming the vias extending vertically between thehorizontal interconnect layers, as follows. Each vertical via opening isformed by etching a hole through an overlying horizontal insulator(silicon dioxide) layer so as to expose a portion of the copperconductor in the underlying horizontal interconnect layer. It is thisexposed portion to which connection is to be made through the via. Abarrier layer must be deposited on the interior surfaces of the viabefore the copper conductor can be formed in the via, to prevent coppermigration as explained above. This barrier layer, in covering allinterior surfaces of the via, covers the exposed portion of theunderlying copper conductor. Since the barrier layer is an inferiorconductor, it must be selectively removed from the underlying copperconductor (in an etch process) without removing the remainder of thebarrier layer from the other interior surfaces of the via. This removalstep has required interruption of the physical vapor deposition processin order to place the wafer in an etch chamber where the step ofselectively removing the barrier layer from the underlying coppersurface is carried out. The wafer is then returned to a physical vapordeposition reactor for formation of the copper conductor(s).

The interruption represented by the selective removal of the barrierlayer entails a higher production cost and consumes production time. Inrecent years, a dual purpose reactor was developed capable of bothphysical vapor deposition of the barrier layer and selective removal ofthe barrier layer after the barrier layer formation step, withoutremoving the wafer from the reactor. As a result, great savings inproduction cost and production time have been realized. This wasaccomplished by providing in the physical vapor deposition chamber aseparate coil near the wafer. After barrier layer formation, the coil isused to form an inductively coupled plasma which selectively sputtersthe barrier layer from horizontal surfaces (i.e., the floor formed bythe underlying copper conductor). Such selective sputtering (hereinafterreferred to as “re-sputtering”) is achieved by applying RF bias power tothe wafer to achieve an ion velocity distribution that is predominantlyvertical. While this dual-purpose reactor works extremely well, it doesentail some additional expense. For example, since the barrier layerdeposition step involves sputtering a metal targets and thereforedeposits metal over all interior surfaces of the reactor chamber, there-sputtering coil must be located inside the chamber so that nometallized surfaces shield the coil or otherwise prevent inductivecoupling of RF power from the re-sputtering coil to the plasma. In orderto avoid process contamination, the re-sputtering coil is formed of puretantalum, adding cost. The coil is subject to very large temperaturefluctuations during its lifetime, and must be changed periodically. RFpower must be coupled to the re-sputtering coil through the vacuum sealof the reactor chamber and through an environment that periodically iscompletely filled with metal vapor. Therefore, an RF feedthrough must beemployed that can tolerate the metal deposition, and whose exteriorsurfaces are textured to avoid excessive accumulation of depositedmaterials and flaking, and that can tolerate wide temperature excursionsover its lifetime.

Another well-known dual-purpose reactor employs an external inductivecoil overlying a portion of the ceiling not blocked by the metal sputtertarget. One problem is that the metal vapor deposition process can coatthe ceiling with metal and thereby block inductive coupling from thecoil antenna. A more significant problem is that the RF plasma producedby the coil produces a high proportion of metal ions from the target, sothat the wafer bias cannot be optimized for etch selectivity tohorizontal surfaces without impacting (de-optimizing) the flux of metalions/vapor from the target. Therefore, the metal deposition process andthe re-sputter process must be performed at separate times.

It should be noted that although such dual purpose reactors are capableof performing both the Ta/TaN barrier layer deposition step and there-sputtering step, a different reactor is typically employed to performthe subsequent copper deposition step. This is because a high flux ofcopper ions on the wafer is desired, and the PVD reactor must bespecially configured in order for the sputtered copper atoms toself-ionize in a very dense plasma at the copper target. Specifically, avery high D.C. power level (40-56 kwatts) is applied to the coppertarget and a specially configured magnetron is employed for a moreconcentrated plasma at the target. Because of the high density of copperions near the target, it is placed very high above the wafer (390 mm),which limits the copper deposition rate to an acceptable threshold (aswell as providing some beneficial collimation of copper neutrals).Typically, however, are large share of the copper ions are deposited onshields in the chamber and otherwise lost while traveling over this longdistance.

In addition to the requirement for a copper PVD chamber and a barrierPVD chamber, a third chamber, an etch chamber, must be employed to carryout a pre-deposition cleaning process, since the copper PVD chamber andthe barrier PVD/re-sputter chamber are not suitable for clean/etchprocesses.

Another problem is the tendency of the tantalum and/or tantalum nitridematerial deposited during formation of the barrier layer to deposit withnon-uniform thickness along the via walls, and in particular toaccumulate faster near the top corners of the vertical walls and therebyexhibit some tendency toward pinch-off. This makes it necessary torestrict the process window in order to ameliorate such problems. Thisproblem is solved to some extent when, upon completion of the barrierlayer deposition process, the re-sputtering process is performed,because the re-sputtering process tends to remove tantalum or tantalumnitride-from the tops and corners of the via walls faster thanelsewhere, while transferring tantalum (or tantalum nitride) materialremoved from the horizontal surfaces (floors) of the vias onto the lowerportions of the via sidewalls. Nevertheless, it would be beneficial toavoid altogether the initial non-uniform tantalum or tantalum nitridedeposition problem, to eliminate any risk of pinch-off, permitting someliberalization of the process window.

It would also be beneficial to avoid the necessity of the internalre-sputtering coil provided at least some of its benefits could berealized in a simpler manner.

The present invention provides benefits at least approaching thoseafforded by the internal re-sputtering coil without the need for such acoil. The present invention furthermore provides a way of amelioratingor avoiding non-uniform deposition of the barrier layer, and a way ofavoiding or minimizing deposition of the barrier layer on the exposedcopper conductor surface forming the floor of the via during formationof the barrier layer.

Another problem that is to be solved is that, as technological advancesdictate smaller geometries and higher aspect ratios for vias and otherfeatures, the degree of ionization of the sputtered material (e.g.,copper) must be increased to achieve the requisite conformality of thedeposited film. Such an increase in ionization requires greater VHFpower applied to the wafer support pedestal. Increased demands onprocess performance require that the temperature of the workpiece bemore precisely controlled, dictating the use of an electrostatic chuckto clamp the wafer to a temperature-controlled surface. Use of anelectrostatic chuck limits the amount of VHF power that can be appliedto the wafer. This is, in large part, because the electrode to which RFpower is applied in the electrostatic chuck typically consists of asmall molybdenum mesh within an aluminum nitride puck. The small gaugeof the mesh (e.g., 100 microns) greatly limits the efficiency of themesh as an RF radiator and limits the amount of RF power that can beapplied to the mesh to as low as 1.5 kW maximum. The requisite degree ofionization for conformal deposition on high aspect ratio openings ofsmall feature sizes (e.g., 45 nm) can only be achieved with much higherVHF power, e.g., 3.5 kW or higher.

SUMMARY OF THE INVENTION

A physical vapor deposition reactor includes a vacuum chamber with asidewall, a ceiling and a retractable wafer support pedestal near afloor of the chamber, and a vacuum pump coupled to the chamber, theretractable wafer support pedestal having an internal electrode and agrounded base with a conductive annular flange extending from the base.A metal sputter target at the ceiling is energized by a high voltageD.C. source. The reactor has an RF plasma source power generator with afrequency suitable for exciting kinetic electrons is coupled to eitherthe sputter target or to the internal electrode of the pedestal. Aremovable shield protects the sidewall and is grounded by pluralcompressible conductive tabs dispersed at generally uniform intervals onthe annular flange and engaging a bottom edge of the shield whenever theretractable wafer support pedestal is in an unretracted position, eachof the uniform intervals being less than a wavelength corresponding tothe frequency of the RF plasma source power generator.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cut-away side view of a plasma reactor embodying theinvention.

FIG. 2 is an enlarged cut-away view of a wafer support pedestal inaccordance with one aspect.

FIG. 3 is an enlarged cut-away view of a wafer support pedestal inaccordance with another aspect.

FIG. 4 illustrates the use of two different plasma bias powerfrequencies in the reactor of FIG. 1.

FIG. 5 is a graph illustrating the combination of the different ionenergy distributions of the different bias power frequencies in theembodiment of FIG. 4.

FIGS. 6A through 6E are sequential cross-sectional views of a portion ofan integrated circuit, in accordance with a process of the invention.

FIG. 7 is an enlarged cross-sectional view of a barrier layer formed inthe process of FIGS. 6A through 6E.

FIGS. 8A through 8C illustrate the formation of a barrier layer in oneembodiment of a process of the invention.

FIGS. 9A and 9B illustrate the formation of a barrier layer in thepreferred embodiment of a process of the invention.

FIG. 10 is a block flow diagram of a preferred process of the invention.

FIGS. 11A, 11B and 11C are cross-sectional side views of an narrowopening through a dielectric layer, and depict deposition results inthree respective modes of the reactor of FIG. 1, namely a conformalmode; a non-conformal mode and a punch-through mode, respectively.

FIG. 12 illustrates a plasma reactor in accordance with a firstalternative embodiment.

FIG. 13 illustrates a plasma reactor in accordance with a secondalternative embodiment.

FIG. 14 illustrates a plasma reactor in accordance with a thirdalternative embodiment.

FIG. 15 illustrates a plasma reactor in accordance with a fourthalternative embodiment.

FIG. 16 illustrates a plasma reactor in accordance with a fifthalternative embodiment.

FIG. 17 depicts a process in which the reactor of FIG. 1 performs apre-deposition cleaning process, a dielectric barrier layer depositionprocess and a metal barrier layer deposition process on the same wafer.

FIGS. 18A and 18B illustrate one embodiment of an RF groundingconductive tab of FIG. 2.

FIG. 19 is a diagram of a first preferred embodiment of a PVD reactorhaving an electrostatic chuck and a highly efficient VHF radiator andemploying a rotating magnet array on the sputtering target.

FIG. 20 is a top view corresponding to FIG. 19.

FIG. 21 depicts the toroidal magnetic confinement pattern of the magnetarray of FIGS. 19 and 20.

FIG. 22 is a diagram of a second preferred embodiment of a PVD reactorhaving an electrostatic chuck and a highly efficient VHF radiator andemploying a rotating magnet array on the sputtering target.

FIG. 23 depicts a first pattern of RF feed columns on the sputter targetof the reactor of FIG. 22.

FIG. 24 depicts a second pattern of RF feed columns on the sputtertarget of the reactor of FIG. 22.

FIGS. 25, 26 and 27 depict first, second and third alternativeembodiments, respectively.

FIG. 28 depicts a process for carrying out physical vapor deposition inaccordance with one aspect of the invention.

FIG. 29A is an elevational view of a plasma reactor in accordance withone embodiment of the invention.

FIG. 29B is a perspective view corresponding to FIG. 29A.

FIG. 29C is a top view corresponding to FIG. 29A.

FIG. 29D is a top view corresponding to an alternative embodiment ofFIG. 29A.

DETAILED DESCRIPTION OF THE INVENTION

A plasma reactor forms barrier layers (such as a tantalum/tantalumnitride film or titanium/titanium nitride film) for conductors (such ascopper, for which the barrier should be tantalum/tantalum nitride) intrenches or through vias between successive interconnection layers of anintegrated circuit. The plasma reactor is capable of both physical vapordeposition and of highly selective re-sputtering to remove barriermaterial from the exposed horizontal surfaces of the underlyingconductor constituting the floor of the via. Significantly, the reactoraccomplishes all this without an internal coil that had previously beenrequired for a fully and precisely controllable re-sputtering step.Instead, a plasma is formed near the wafer to perform the re-sputteringstep. For this purpose a process gas such as argon may be introduced andsource power is applied to the wafer at an RF frequency effective forcapacitively coupling energy to kinetic electrons to excite argon plasmaions near the wafer. The term “source power” as employed in thisspecification refers to RF power suitable for maintain an RF-coupledplasma by coupling power to kinetic electrons in the plasma. This is tobe distinguished from use of the term “source” when referring to theD.C. excited metal sputtering target, which is the “source” of the metalatoms or ions in a metal deposition process. Typically, the source powerfrequency is a VHF frequency because of the low mass-to-charge ratio ofelectrons. The ions of the VHF-coupled plasma formed near the wafer areemployed in the re-sputtering step. The selectivity of the re-sputteringstep for horizontal surfaces is established by applying bias power tothe wafer at an RF frequency effective for coupling energy to the ions(e.g., argon ions), which is typically an HF or LF frequency because ofthe high mass-to-charge ratio of the ions. This constricts the ionvelocity distribution across the plasma sheath at the wafer surface to asmall directional range about the chamber axis, typically a verticaldirection, making the re-sputtering step highly selective for surfacesperpendicular to the chamber axis, typically horizontal surfaces. Asignificant feature is that the bias power controls the selectivity ofthe ion re-sputter or etch step without affecting the flux of metalatoms from the target toward the wafer. This is facilitated by a lowpower (2-5 kW) D.C. discharge plasma at the target surface whichproduces primarily neutral metal particles or atoms from the target thatare unaffected by the bias power applied to the wafer. Thus, twodifferent plasmas are employed, one being a D.C. discharge plasma at thetarget and the other being an RF (VHF) plasma at the wafer. Therefore,the target sputtering may be optimized without affecting there-sputtering plasma at the wafer, while the bias voltage may beoptimized without affecting the target sputtering. This feature is notpossible in conventional ion physical vapor deposition reactors thatemploy RF coupled plasmas near the target to produce metal ions for thephysical vapor deposition process.

An advantageous mode is provided that is unique to the present inventionin which the physical vapor deposition and the re-sputtering can beperformed simultaneously, and the selectivity of the re-sputter or etchprocess is adjusted without affecting the flux of metal atoms from thetarget.

The re-sputtering step tends to compensate for non-uniform deposition ofthe barrier layer material. Therefore, in one embodiment of theinvention, the re-sputter step is performed simultaneously with thebarrier deposition step. This is possible because a preferred embodimentof the invention produces two somewhat independent plasmas, namely aD.C. discharge plasma near the ceiling or target that is confined by amagnetron above the target and an RF plasma near the wafer surface toperform the re-sputtering. Thus, the plasma near the ceiling isoptimized for sputtering the target while (simultaneously) the plasma atthe wafer is optimized for re-sputtering and selectively etching thefloor of each via. One advantage is that prominent non-uniformities inthe deposited barrier layer film are reduced or are never formed,thereby reducing the risk of pinch-off or other problems in the vias.Another advantage of this embodiment is that throughout the entirebarrier deposition/re-sputter process, accumulation of barrier materialcan be entirely avoided on the exposed horizontal surface of theunderlying conductor forming the floor of the via. This is accomplishedby adjusting the barrier material deposition rate (controlled largely bythe tantalum target D.C. sputter voltage) relative to the re-sputterrate (controlled largely by the VHF plasma source power applied to thewafer.)

The invention can afford certain advantages depending upon itapplication. For example, a low power (2-5 kW) D.C. power level isemployed to sputter the metal target for all deposition process,including copper, tantalum and titanium, because metal neutrals aredesired. Therefore, the target height above the wafer and the magnetrondesign are the same in all these processes, so that the same chamber canperform any or all of them. The target height above the wafer can berelatively low, or between about 225 mm and 290 mm, for example. Inaddition, the VHF source power applicator and the HF bias powerapplicator can be used without a target to excite a plasma (such asargon plasma) to perform a pre-deposition clean process prior to eachdeposition process. Such a pre-clean process can be repeated prior toeach and all of the deposition steps, including the barrier metal(tantalum) deposition step, the barrier dielectric (tantalum nitride)barrier deposition step, the copper seed layer deposition step and thecopper conductor deposition step.

Reactor Apparatus:

Referring to FIG. 1, a reactor of a first embodiment of the inventionincludes a vacuum chamber defined by a cylindrical side wall 10, adisk-shaped ceiling 12, and a wafer support pedestal 14 for supporting asemiconductor wafer 16 to be processed. A target 18 of a metal (e.g.,tantalum) to be deposited on the wafer 16 is mounted on the ceiling 12.A process kit consisting of a cylindrical shield 20 surrounds the wafer16 and the target 18. A magnetron 22 of the conventional type overliesthe target 18 on the external side of the ceiling 12. A high voltageD.C. source 24 is coupled to the target 18. A process gas injector 26furnished process gas from a supply 28 into the interior of the chamber.A vacuum pump 30 maintains a desired sub-atmospheric pressure in thevacuum chamber.

The wafer pedestal 14 is coupled through an impedance match network 34to a VHF plasma source power generator 36 and to an HF or LF plasma biaspower generator 38. The high voltage D.C. source maintains an upperplasma 40 near the target 18. The VHF plasma source power generator 36maintains a lower plasma 42 at or near the surface of the wafer 16. Thetwo plasmas 40, 42 may be maintained simultaneously or may be producedat different times. The upper plasma 40 is a D.C. discharge plasma thatenables sputtering of the target 18 to produce mainly neutral metalatoms from the target 18 that deposit on the wafer, with some metal ionsfrom the target 18. The lower plasma 42 is a capacitively coupled RFplasma that promotes selective etching of horizontal surface on thewafer 16. The two plasmas 40, 42 may be controlled independently, forseparate control of the metal deposition process and the re-sputterprocess. The LF bias power applied to the wafer determines theselectivity of the re-sputter/etch process for horizontal surfaces.Plasma uniformity, particularly uniformity of the plasma 42 nearest thewafer, is controlled by an electromagnetic coil 43 wrapped around thecylindrical sidewall of the reactor chamber and supplied with D.C.current by a current source controller 45.

Coupling of the VHF source power and HF or LF bias power to the wafer isillustrated in FIG. 2. The wafer support pedestal 14 can be anelectrostatic chuck (ESC) for electrostatically holding the wafer 16 inplace. In this case, the ESC or pedestal consists of an insulating layer50 mounted on a conductive base 51 and an electrode 52 such as aconductive mesh buried inside the insulating layer 50. The pedestalstructure can extend downwardly in a coaxial arrangement consisting of acenter conductor 54 connected to the electrode 52, an insulatingintermediate layer 56 and an outer conductor 58 connected to theconductive base 51. The conductive base can be coupled to the bottom ofthe cylindrical shield 20 by conductive tabs 60 to provide a morecontinuous ground reference. The center conductor 54 is coupled to theRF power sources while the outer conductor 58 is grounded. The impedancematch network 34 consists of a conventional impedance match circuit 64coupled to the RF (VHF) plasma source power generator 36 and aconventional impedance match circuit 68 coupled to the RF (HF or LF)plasma bias power generator 38. The output of the impedance matchcircuit 64 is connected through a high pass filter 65 to the waferpedestal center conductor 54, while the output of the impedance matchcircuit 68 is connected through a low pass filter 69 to the waferpedestal center conductor 54. In addition, a D.C. chuck voltage source74 is connected to the wafer pedestal center conductor 54 and isisolated from RF power by an isolation capacitor 76. The high passfilter 65 has a sufficiently high cut-off frequency to prevent HF or LFcurrent from the RF generator 38 from reaching the VHF match circuit 64,while the low pass filter has a sufficiently low cut-off frequency toprevent VHF current from the RF generator 36 from reaching the HF (orLF) match circuit 68.

FIG. 3 illustrates another embodiment of the wafer support pedestal 14in which the electrode 52 contacts the wafer, and there is noelectrostatic chucking of the wafer. In this case, since the electrode52 is potentially exposed to the plasma, the electrode 52 can be formedof the material to be deposited on the wafer, such as tantalum.

FIG. 4 illustrates an embodiment in which the bias power consists ofboth HF and LF frequencies (e.g., 13.56 MHz and 2 MHz, respectively, forexample). For this purpose, there are two bias power RF generators,namely an HF bias power generator 38 a and an LF bias power generator 38b, the generators 38 a, 38 b being coupled through respective matchcircuits 68 a, 68 b and filters 69, 69 a to the wafer pedestal centerconductor 54. The VHF source power generator 36 is coupled through itsimpedance match circuit 64 and through the high pass filter 65 to thewafer pedestal center conductor 54. One advantage of this embodiment isthat the lower ion energy distribution of the HF bias and the higher ionenergy distribution of the LF bias (both shown in FIG. 5) can becombined to produce an ion energy distribution that peaks between thepeaks of the LF and HF ion energy distributions. This peak can beshifted up or down in energy by adjusting the relative power levels ofthe LF and HF power generators 38 a, 38 b.

The deposition rate of the target material (e.g., tantalum) is mainlydetermined by the power delivered by the D.C. voltage source to thetarget. The selectivity of the etch/re-sputter process (for horizontalsurfaces) is determined by the bias power, while the rate of theetch/re-sputter process is mainly determined by the source power level.Therefore, there are three parameters that can be controlledindependently of one another, namely metal deposition rate, etchselectivity for horizontal surfaces and etch rate. Since all these canbe controlled independently of one another, the metal deposition andetch/re-sputter process may be performed simultaneously, if desired.

PVD/Re-Sputter Method:

The reactor of FIG. 1 is particularly useful in the formation of metalcontacts between successive interconnection layers of an integratedcircuit. Typically, an integrated circuit includes an activesemiconductor layer having thousands of transistors and many insulatedinterconnection layers stacked over the active semiconductor layer andproviding complex interconnection circuits among the transistors. Theconnections between interconnection layers are formed through vias orvertical holes between the interconnection layers by filling the holeswith a metal such as copper. In order to prevent failure by shortcircuiting due to diffusion of copper through insulating material, abarrier layer of tantalum and tantalum nitride is placed between thecopper and the insulating material. It is in the deposition of thebarrier layer within the via that the reactor of FIG. 1 provides greatadvantage.

FIG. 6A is an enlarged cross-sectional side view of a partiallyfabricated portion of an interconnection layer 100 in a stack of manyinterconnection, layers overlying an active semiconductor layer (nowshown). FIG. 6B is the corresponding top view. The interconnection layer100 includes, among many conductors, a pair of parallel copperconductors 102, 104 embedded in an insulator (silicon dioxide) layer106. Each copper conductor 102, 104 is separated from the dielectriclayer 106 by a barrier layer 108 that prevents diffusion of copper atomsinto the dielectric layer 106. Preferably, the barrier layer 108includes a tantalum nitride layer contacting the insulator layer 106 andcovered by a tantalum layer and a copper seed layer. The structure isbest shown in the enlarged view of FIG. 7, which shows a tantalumnitride layer 110 covering the insulator layer 106, a tantalum metallayer 112 overlying the tantalum nitride layer 110 and a copper seedlayer 114 overlying the tantalum metal layer 112. A copper conductor,such as the copper conductor 102, overlies the copper seed layer 114.The tantalum metal layer 112 establishes a high quality bond with thetantalum nitride layer 110, while the copper seed layer establishes ahigh quality bond with the tantalum metal layer 112 on one side and thecopper conductor 102 on the opposite side.

Before the next interconnection layer is formed on the top surface ofthe insulator layer 106, a vertical opening or via 120 is opened throughthe insulator layer 106, typically by etch processes (FIGS. 6A and 6B).The via 120 consists of a large opening 122 extending only partlythrough the insulator layer 106 and a pair of smaller openings 124extending down to the respective copper conductors 102, 104. Typically,the etching process that forms the two smaller openings 124 is carriedout sufficiently to remove the exposed portion of the barrier layer 108overlying each conductor 102, 104 (FIG. 6A).

The via 120 forms a vertical conductor when later filled with copper.However, before copper is deposited into the via 120, a barrier layer130 is deposited onto all surfaces in the via 120 and onto the topsurface of the insulator layer 106 as shown in FIG. 6C. The barrierlayer 130 has the same structure as that described above with referenceto FIG. 7, including a tantalum nitride layer 110, a metal tantalumlayer 112 and a copper seed layer 114. In one embodiment of theinvention, each sub-layer 110, 112, 114 of the barrier layer 120 isdeposited in a separate step by providing the appropriate material forthe metal target 18 (tantalum for the sub-layers 110, 112 and copper forthe sub-layer 114). The target 18 is sputtered by introducing a processgas which is ionized in the vicinity of the target by the large D.C.sputtering voltage from the sputter voltage source 24. In order todeposit the tantalum nitride sub-layer 110, nitrogen is employed as theprocess gas, and the tantalum atoms combine with nitrogen atoms as theyimpact the wafer to form a tantalum nitride film. When depositing themetal tantalum layer 112 and, later, when depositing the copper seedlayer 114, the process gas is an inert or non-reactive gas, such asArgon. Thus, three deposition steps are carried out. First, using atantalum sputtering target and nitrogen process gas, tantalum nitride isdeposited. Second, using a tantalum target and argon process gas,metallic tantalum is deposited. Third, using a copper target and argongas, a copper seed layer is deposited.

In one embodiment of the invention, no plasma RF (VHF) source power isapplied to the wafer support pedestal 14, although a modest level ofplasma RF (HF or LF) bias power may be applied. In this way, metal issputtered from the target 18 and deposited onto the wafer 16. As aresult, the barrier layer 130 is formed by carrying out the threedeposition steps for the successive sub-layers 110, 112, 114. Thebarrier layer 130 covers all exposed surfaces including the portions ofthe copper conductors 102, 104 exposed by the small openings 124, asshown in FIG. 6C.

After each of the three deposition steps have been completed, anetch/re-sputter step is carried out (FIG. 6D) in which the VHF plasmasource power generator 36 and the HF (or LF) plasma bias power generator38 deliver power to the wafer support pedestal 14. This produces aplasma near the wafer that furnishes ions guided to the horizontalsurfaces by the applied plasma bias power. These ions sputter thehorizontal surfaces to remove films deposited thereon, such as theportion of the barrier layer 130 at the bottom of the small openings124. Within the small openings 124, the close proximity of the verticalwalls (or small diameter of the openings 124) promotes the re-depositionof atoms sputtered from the floor 124 a of each opening 124 onto thevertical side wall. This uncovers the copper conductors, as desired, asillustrated in FIG. 6D. In other areas where there is no vertical wall,such as the vast area of the top surface of the insulator layer 106, thesputtered atoms re-deposit onto the horizontal surface, so that there isno net loss.

In a preferred embodiment, each of the three deposition process steps(corresponding to the three layers 110, 112, 114) is performedsimultaneously with the etch and re-sputter process step. In thispreferred embodiment, the sputter voltage source 24 delivers power tothe target 18, while simultaneously the VHF plasma source powergenerator 36 and the HF (or LF) plasma bias power generator 38 deliverpower to the wafer support pedestal 14. This produces a plasma near thewafer that furnishes ions guided to the horizontal surfaces by theapplied plasma bias power while atoms from the target 18 are beingdeposited. Deposition of atoms from the target 18 on the horizontalsurfaces such as the exposed portions of the copper conductors 102, 104is avoided provided the etch rate on the horizontal surfaces rival thedeposition rate of atoms from the target 18. This condition is realizedby an appropriate adjustment of the voltage of the D.C. sputter voltagesource 24 (to adjust the deposition rate) and of the power level of theVHF source power generator 36. The power level of the HF (or LF) biaspower generator 38 is adjusted to achieve the desired degree of etchselectivity for horizontal surfaces. The result is that the barrierlayer 130 is not formed over the horizontal floor of the via 120, sothat the process sequence skips the state illustrated in FIG. 6C.

The next step (FIG. 6E) is to deposit a thick copper layer to form thenext interconnect layer 200 and vertical conductors extending throughthe via 120 between the lower interconnect conductors 102, 104 and theupper interconnect layer 200, as shown in FIG. 6E.

The sequence illustrated in FIGS. 8A through 8C shows one advantage ofthe re-sputtering step of FIG. 6D. FIG. 8A illustrates one of the smallopenings 124 prior to deposition of the barrier layer 130. FIG. 8B showshow the barrier layer 130 is formed in cases where the re-sputteringstep is not carried out simultaneously with the deposition step.Specifically, the barrier layer 130 tends to accumulate with greaterthickness near the top edge of the small opening 124 and with smallerthickness near the bottom of the opening 124. The re-sputtering stepremoves the excess material from the top edge and removes the materialfrom the floor of the small opening and re-deposits it on the verticalside wall, so that the thickness distribution along the vertical sidewall becomes more uniform, as indicated in FIG. 8C. The problem is thatthe thicker accumulation of barrier material near the top edge of thesmall opening 124 may lead to pinch-off, so that the re-sputter stepcould have no beneficial effect, the device would fail.

This risk is avoided in the preferred method in which the re-sputterstep (FIG. 6D) and the deposition step (FIG. 6C) are carried outsimultaneously. In this preferred mode, the process begins with a newlyformed small opening 124 in FIG. 9A and transitions directly to auniform barrier layer 130 in FIG. 9B. The simultaneousdeposition/re-sputtering prevents the deposition process from formingsignificant non-uniformities in the barrier layer 130. This eliminatesthe risk of the pinch-off effect illustrated in FIG. 8B.

FIG. 10 is a block diagram illustrating the preferred process. In block310 of FIG. 10, a deposition D.C. discharge plasma is generated aroundthe target 18 (near the ceiling) to deposit atoms from the target ontothe wafer. In block 312, a re-sputter capacitively coupled RF plasma isgenerated near the wafer to produce ions to bombard the wafer tore-sputter the deposited atoms from the target 18. In the step of block314, plasma RF bias power is applied to the wafer. The bias power issufficient to render the sputtering highly selective for horizontalsurfaces. In block 320, the plasma source power applied to the wafer andthe D.C. sputter voltage applied to the target are adjusted relative toone another so that the re-sputter rate is at least nearly as great asthe sputter deposition rate.

One embodiment of the PVD/re-sputter reactor of the invention is capableof depositing three different type of layers by operating in threedifferent modes, specifically, in mode (A), a highly conformal layerwith uniform sidewall and horizontal surface coverage, in mode (B), anon-conformal layer with little or no sidewall coverage, and in mode(C), a “punch through” layer with good sidewall coverage and goodhorizontal surface coverage in a large field, but no coverage of bottomsurfaces of high aspect ratio openings. The conformal layer of mode (A),illustrated in FIG. 11A, is obtained by applying a relatively low levelof D.C. power to the target (e.g., 5 kW), high VHF source power to thewafer (1 kW at 60 MHz) and a low level of HF bias power to the wafer(about 100 W at 13.56 MHz). The non-conformal layer of mode (B),illustrated in FIG. 11B, is obtained under the same conditions exceptthat the HF bias power level is reduced to zero. The “punch-through”layer of mode (C), illustrated in FIG. 11C, is obtained by increasingthe bias power to a high level (500 W at 13.56 MHz). The conformal modeis particularly useful for depositing the copper conductor layer. Thenon-conformal mode is particularly useful for covering the bottom orfloor of a via with a low-resistance metal such as tantalum or titanium.The punch-through mode is the preferred mode for depositing the barrierlayer (Ta and TaN) in a via.

In some cases, the plasma density distribution may differ between thethree modes described above. In order to maintain more uniform plasmadensity distribution, the current source controller 45 may causedifferent levels of D.C. current to flow through the electromagnet coil43 in different ones of the three modes. In any case, the current levelfurnished by the current controller 45 is preferably optimized toimprove the radial plasma ion density uniformity in the process zone.

Each of the three modes described above with reference to FIGS. 11A, 11Band 11C may be implemented by a process controller 210 shown in FIG. 1whose outputs control the power level of the target high voltage D.C.supply 24, the power level of the VHF plasma source power generator 36and the power level of the HF or LF bias power generator 38. The processcontroller 210 may be controlled by a user through a user interface 212,allowing the user to program the controller to have the reactor of FIG.1 automatically transition between any of the operating states definedabove for the conformal mode, the non-conformal mode and the punchthrough re-sputter mode. The process controller (or processor) 210therefore has three states to which the user may set or program theprocessor 210 to enter into. One state is the conformal deposition modein which the processor 210 sets the D.C. power level of the supply 24 toa low level, sets the power level of the VHF generator 36 to a highlevel and the HF/LF bias generator 36 to a low level. The another stateis the non-conformal mode in which the processor 210 sets the D.C. powerlevel of the supply 24 to a low level, sets the power level of the VHFgenerator 36 to a high level and the HF/LF bias generator 38 to zero (ornearly zero) level. The, remaining state is the punch through state inwhich the processor 210 sets the D.C. power level of the supply 24 to alow level, sets the power level of the VHF generator 36 to a high leveland the HF/LF bias generator 38 to a high level.

The processor 210 may also govern the electromagnet current source 45,so that in each of the three modes (FIGS. 11A, 11B, 11C), the currentlevel is optimized for a more uniform radial distribution of plasma iondensity distribution.

The metal target 18 may assume a shape different from the disk shapeillustrated in FIG. 1. For example, as shown in FIG. 12, a modifiedtarget 18′ having an annular shape may be employed, leaving a centerportion 12 a of the ceiling 12 exposed and an annular portion 12′blocked by the target 18′. The overlying magnetron 22′ has acorresponding annular configuration. Optionally, VHF plasma source powermay be applied to the ceiling center portion 12 a by an additional VHFsource power generator 36′ (dashed line in FIG. 12). This may be inaddition to or in lieu of the VHF source power generator 36 coupled tothe wafer support pedestal 14. However, it is preferred to couple VHFsource power to the pedestal 14 rather than to the ceiling 12.

FIG. 13 depicts another option, in which a coil antenna 400 may beplaced over the ceiling center portion 12 a and coupled to an RF sourcepower generator 410 through an impedance match circuit 415 to produce aninductively coupled plasma. A louvered shield 420 may cover the ceilingcenter portion 12 a during metal deposition to avoid metal coverage ofthe ceiling center portion 12 a, so that the coil antenna 400 will notbe shielded from the plasma.

FIG. 14 illustrates how the configuration of the coil antenna 400 andtarget 18′ may be reversed from that illustrated in FIG. 13. In FIG. 14,the coil antenna 400 is in an annular shape while the disk-shaped target18 is located at the ceiling center portion 12 a. The reactor of FIG. 14may be modified as follows: The annular coil antenna 400 may be removedand the peripheral portion 12′ of the ceiling 12 may be conductive andcoupled to the VHF plasma source power generator 410 through theimpedance match circuit 415, as indicated in dashed line in FIG. 14.

FIG. 15 illustrates another alternative embodiment in which the target18 is configured in an inverted cup shape. As shown in FIG. 16, the cupshape may be of sufficient height to accommodate an array of magnets 450along its side to enhance ion distribution.

FIG. 17 is a flow diagram of a process carried out in the PVD/re-sputterchamber of FIG. 1. In the step of block 1710, a pre-clean process isperformed by applying no power to the metal target, introducing anetchant precursor gas such as a fluorine-contain gas or a neutral gassuch as argon, applying sufficient VHF plasma source power to the waferfrom the VHF generator 36 and applying a small amount of HF bias powerto the wafer from the HF generator 38. In the following step of block1720, the dielectric film (e.g., TaN) of a barrier layer is deposited byintroducing nitrogen gas and sputtering the metal target (e.g.,tantalum) while re-sputtering by maintaining the VHF-driven argon plasmanear the wafer and applying bias power to the wafer. In the next step(block 1730), the metal film of the barrier layer is deposited bystopping the supply of nitrogen gas, so that pure metal is depositedwhile the VHF-driven argon plasma performs re-sputtering. Thus, threesuccessive processes may be performed in the PVD re-sputter reactor ofFIG. 1 without removing the wafer from the reactor.

Use of the shield 20 in the reactor of FIG. 1 with the VHF source powersupply 36 can be problematic. This is because process control can belost due to uncontrolled plasma generation on the outside of the shield.This can occur because the RF return path for plasma near the waferperiphery is along the inside (wafer side) surface of the shield 20 andup to the top of the shield 20, and then down the inside surface of thechamber side wall 10 (traveling the entire height of the side wall 10)and along the bottom of the chamber body to the wafer support pedestal14. At a VHF frequency such as 60 MHz, this RF return path exceeds morethan one wavelength, so that along the path there will be severalstanding wave peaks of the VHF source power at which plasma is likely tobe generated. To the extent such a peak falls on the outside of theshield 20, plasma will be generated on the outside of the shield 20,outside of the wafer processing zone enclosed by the shield 20. Suchuncontrolled plasma generation will divert RF source power from thewafer process, causing a loss of process control.

This problem is solved by providing the RF connection bridge orconductive tab 60 referred to above with reference to FIG. 2. The RFconnection bridge provides an extremely short RF return path between thebottom edge of the shield 20 and the conductive base 51 of the wafersupport pedestal 14. The RF return path for plasma over the wafer 16near the bottom of the shield 20 is therefore much shorter than the VHFsource power wavelength, so that there are no standing wave peaks alongthe shield, and therefore no undesirable plasma generation along surfaceof the shield 20.

FIGS. 18A and 18B illustrate a preferred embodiment of the connectionbridge or tab 60 as an elastically deformable cylindrical spring 224formed of a conductive material (e.g., copper). The cylindrical spring224 is supported on a conductive table 226 that is connected to theconductive base 51 of the wafer support pedestal 14. As shown in FIG.18A, when the pedestal 14 is raised to the top position (where it isheld during processing), the cylindrical spring 224 is pressed againstthe bottom edge of the shield 20 so as to be elastically deformed to atleast partially conform with the shape of the bottom corner of theshield 20, thereby providing a very low resistance connection to theshield 20. This path extends from the shield 20 through the tab 60 andradially along the base 51 to the coaxial outer conductor 58 of thecoaxial RF feed to the pedestal. In FIG. 18B, the pedestal 14 has beenwithdrawn to a lower position, allowing the cylindrical spring 224 toreturn to its undeformed cylindrical shape. The cylindrical axis of thespring 224 lies generally parallel with the plane of the wafer 16.

Copper Deposition Using a Single VHF Frequency:

The reactor of FIG. 1 may be used to deposit copper, such as the copperseed layer 114 of FIG. 7, for example. This is accomplished by usingcopper instead of tantalum as the metal target 18 in the reactor ofFIG. 1. However, using the reactor of FIG. 1 for copper depositioninvolves special problems. One problem involves undesirable formation(during copper deposition) of an overhanging copper protrusion or “neck”on the sidewall of each narrow aspect ratio opening or via (of the typeillustrated in FIG. 8B). Specifically, it is more difficult in a copperdeposition process to prevent formation of a metal neck or protrusion onthe sidewall. The neck is formed from copper sputtered from the topcorner edge of the opening onto the opposing surface of the sidewall.Such an overhanging metal formation neck near the top of the opening(FIG. 8B) tends to protrude into the narrow opening or via, eventuallyenclosing an unacceptable void at the bottom of the opening by closingoff the opening. Sputtering is mainly caused by the carrier gas (Argon)ions. Sputtering of the top corner edge of the via or narrow opening isvery high relative to other features because the sputtering rate ismaximum for ion incidence angles between 30 and 50 degrees. Using acarrier gas such as Argon to promote the formation of kinetic electrons(for VHF plasma generation near the wafer), we have found it difficultto find a process window of power levels of the VHF and HF power sources36, 38 in which overhang formation or close-off of the opening isavoided. It seems that the HF bias power required to direct a sufficientflux of copper atoms to the bottom of the via opening (for good bottomcoverage) has the undesired effect of creating intense re-sputtering ofcopper from the top corner edge of the narrow opening onto the opposingsidewall surface of the opening to create the problematic copperprotrusion on the sidewall (resulting in a deposition profile similar tothat illustrated in FIG. 8A). As the sidewall protrusion grows, it canpinch-off the opening thereby preventing deposition of copper on thefloor of the-opening. This problem likely is caused by two factors:

First, such harmful re-sputtering of the copper from the top corner edgeis worse at higher ion energy levels. This is a serious problem becausethe HF and LF bias power frequencies of FIG. 1 produce a wide ion energydistribution having significant components at very high ion energies(e.g., an ion energy component corresponding to the peak-to-peak biasvoltage).

Secondly, selection of a bias power level sufficient to accelerate asufficient amount of copper ions to the via floor necessarilyaccelerates many more times that number of argon atoms to the wafer,which sputter away the copper atoms from the top corner edge of thenarrow opening. This happens because copper and argon have (for presentpurposes) fairly similar atomic masses, so that the effect of the biasvoltage in accelerating ions across the plasma sheath at the wafer willbe about the same for both copper and argon. This is problematicbecause, due to the limited efficiency of the target 18 of FIG. 1 as asource of copper, there can be one (or more) orders of magnitude moreArgon ions present than Copper ions, so that Argon sputtering of Copperoverwhelms the deposition process. In some cases, sputtering by Argonions can also reach the via floor and compete with copper deposition onthe via floor.

We have solved this problem (at least for 65 nm feature size designrules) by applying only VHF source power from the VHF source 36 whileapplying no HF or LF bias power from the HF/LF source 38. In thepreceding description of this specification, a similar mode of operationof the reactor of FIG. 1 was mentioned in which no HF or LF bias poweris applied. At nominal VHF power levels (e.g., 100 Watts to 300 Watts),such a mode produces a non-conformal metal deposition (characterized bya relatively thin sidewall coverage) due to lack of re-sputteringwithout HF or LF bias power.

However, this mode is rendered highly conformal by compensating for thelack of HF or LF bias power by increasing the VHF source power level toa medium level or a high level, until achieving a requisite flux of ionsperpendicular to the wafer surface (i.e., parallel to the axis of eachhigh aspect ratio opening) to obtain the desired re-sputtering effects.We have found this achieves the highly conformal effects of thenow-missing HF or LF bias power. We have discovered that the lack of HFor LF bias power may be completely compensated by increasing the VHFsource power level in this manner. This is believed to be because theVHF source power level from the VHF source 36 of FIG. 1 may be increasedto the point at which good via floor coverage from direct copperdeposition and good sidewall coverage by copper re-sputtering isobtained. (The re-sputtering effect is discussed at length in previousportions of this specification.) This is possible because increasing theVHF source power level does not significantly increase ion energy butmainly increases the flux of copper ions. This is particularly true ifthe VHF source power frequency is particularly high, e.g., 60 MHz.Increasing source power at such a VHF frequency does not appreciablyincrease ion energy at the wafer surface because the frequency is toohigh for ions to follow the oscillations. Instead, the principal portion(or all) of the source power is consumed in generating kinetic electronsfrom the carrier gas (which are sufficiently light to follow the sourcepower oscillations). This principal portion is preferably-greater thanat least 50%. This principal portion may be around 80% at a source powerfrequency of 60 MHz. As a result, the undesirable effects of HF or LFbias power are avoided while conformal copper deposition is achieved.

The increase in VHF power required to achieve the foregoing effect maybe significant. The nominal power range of VHF power at which depositionis non-conformal lies in a range of about 50-300 Watts, depending uponchamber design and other process parameters (pressure, gas composition,gas flow rate, etc.). The desired degree of deposition conformality maybe achieved in this novel single frequency conformal mode by increasingthe VHF power to a medium level, between approximately 300 to 800 Watts.In some cases, it may be necessary to increase the VHF power to a highlevel (800-1500 Watts) before realizing a desired degree ofconformality. The increase in VHF power required to carry out thissingle frequency conformal mode is readily ascertained empirically bymeasuring deposition conformality at increasing VHF power levels.

In summary, a new copper deposition mode of the reactor of FIG. 1 is onein which the metal target 18 is copper, and the only RF power sourceemployed is the VHF plasma source power supply 36. No plasma bias poweris applied (i.e., RF power having a sufficiently low frequency to befollowed by ions such as copper). In this single frequency mode, the VHFsource power level is increased to reach a high degree of conformalityin the deposited copper layer. Specifically, the VHF source power isincreased until a sufficient flux of copper ions at the wafer isachieved to provide good copper coverage on the floors of high aspectratio openings with sufficient re-sputtering to provide adequatesidewall copper coverage. As in the other modes disclosed previously inthis specification, the High Voltage D.C. supply 24 and the magnetron 22need only provide a medium amount of power, and the copper plasmagenerated near the target 18 may or may not be self-ionizing.

Dual Frequency Copper Deposition Modes:

While the single frequency copper deposition mode described immediatelyabove is effective at feature sizes as small as 65 nm, it is felt thatcopper deposition at smaller feature sizes (e.g., 45 nm, 35 nm) are bestaccomplished using an HF or LF bias in combination with VHF sourcepower. As discussed above, the VHF power may be increased to increasethe flux of copper ions without a proportionate increase in ion energy.This advantage is enhanced by increasing the VHF source power frequencyfrom 60 MHz to 81 MHz. With such an elevated frequency, the principalportion of the source power dedicated to kinetic electron generation (togenerate plasma ions) is as high as 90% or 95%, almost none of itincreasing ion energy. Thus, the VHF source power level may be increasedto an even greater degree (without a significant harmful increase in ionenergy) in order to increase copper ion flux at the wafer to increasecopper deposition at the via floor and enhance uniform copperre-sputtering for uniform deposition on the via side walls. This featurereduces the required HF bias power level for a conformal copperdeposition. For example, the required HF power level may be reduced from5 kwatts to 3 kWatts, and in some cases to even lower levels (e.g., 1 kWatt). By reducing the HF bias power level, undesirable coppersputtering by ions of the carrier gas (e.g., argon) is reducedaccordingly. It should be noted that the HF bias power is of asufficiently low frequency so that ions near the plasma sheath readilyfollow its oscillations so that nearly all of its power is consumed inaccelerating ions toward the wafer and thereby increasing ion energy.

In order to regulate or prevent re-sputtering of the copper from the topcorner via edge to the via sidewall by ions of the carrier gas (e.g.,argon ions), a carrier gas is employed having a much lower atomic massthan copper. Specifically, a light inert gas (helium) is employed as thecarrier gas. Although helium has a low atomic mass, it neverthelesssuffices nearly as well as argon to produce, under the stimulation ofthe VHF source power, sufficient kinetic electrons to produce anadequate copper plasma near the wafer surface. If the carrier gas ionsare much lighter than the copper ions, then they do not sputter copperatoms from the via top corner edge onto the via sidewall at such a fastrate. This feature therefore achieves enhanced control of there-sputtering process. In some embodiments employing a higher bias powerlevel, there is an additional problem of Argon ions sputtering depositedcopper atoms from the via floor faster than the copper deposition rate.This additional problem is solved by using the lighter (Helium) carriergas, because the lighter Helium atoms do not produce such a high coppersputter rate. As a result, the re-sputtering of copper from the topcorner via edge to the via sidewall is better regulated or controlled.Furthermore, the additional problem (encountered in some cases) ofremoving copper from the via floor by the more populous carrier gas ionsis eliminated or at least reduced. An inert gas such as helium isselected because it introduces no additional chemical reactions oreffects and does not chemically react with the deposited copper.

Another problem unique to copper deposition is that the surface of thedeposited copper has a relatively high surface energy, and is active(like a fluid) during plasma enhanced deposition, enabling it to reduceits surface energy by accumulating into small globs or balls of copperon the surface. The result is formation of a low-quality copper surface.This problem is solved by adding to the carrier gas a species thatcombines with copper bonds on the deposited copper surface (on thewafer) to reduce the copper surface energy. The preferred choice forsuch a surface energy-reducing agent is hydrogen. In the helium plasma,diatomic hydrogen molecules dissociate into monatomic hydrogen, whichadheres to open copper atomic bonds in the surface of the depositedcopper layer. This surface reaction reduces the copper surface energy,allowing the deposited copper atoms to flow during deposition in thinuniformly flat layers, thereby forming a uniformly smooth high qualitycopper surface.

This embodiment is also effective for removing copper oxide from thedeposited copper, or for preventing formation of copper oxide duringprocessing. In removing copper oxide, the hydrogen reduces the copperoxide, capturing oxygen atoms to form water molecules that are releasedinto the chamber.

The hydrogen gas may form as much as 10% of the process gas. If thereactor is specially constructed to handle pure hydrogen gas, thenhydrogen gas may constitute all or nearly all of the process gas.

The bias power window or range within which the copper deposition rateat the 65 nm via floor exceeds the neck growth rate on the sidewall is a“65 nm window”. The bias power window or range within which the copperdeposition rate at the 45 nm via floor exceeds the neck growth rate onthe sidewall is a “45 nm window”, which is significantly narrower thanthe 65 nm window because of the greater aspect ratio of the opening.Within each of these windows, the copper floor deposition rate exceedsthe sidewall neck growth rate sufficiently to allow copper deposition onthe via floor to reach a target thickness (e.g., 50-500 Angstroms)before the sidewall copper neck pinches off the opening. The problem wasthat these windows either did not exist or were too narrow for practicaloperation.

One way in which the process window is widened in the present inventionis by increasing the VHF source power level, which increases the flux ofcopper ions without a concomitant increase in sputtering or neck growthrate. Another way of widening the process window is to employ alow-atomic mass carrier gas species (Helium). This tends to decrease theneck growth rate by reducing sputtering. Using a low atomic mass carriergas also tends to increase the copper deposition rate at the via floor,by preventing the removal of deposited copper from the floor surface bysputtering from the carrier gas.

Another advantage of the VHF source power is that it further widens theprocess window by at least partially masking the nonuniformity in radialdistribution of the HF (or LF) bias power. In some cases, bias powerradial distribution is non-uniform across the wafer surface, whichrestricts the allowable. RF power range (to avoid exceeding processlimits in any radial location on the wafer), thereby narrowing the biaspower process windows. At least partially masking this nonuniformity byapplying VHF source power reduces this effect, thereby preserving awider process window.

In summary, a highly conformal layer of copper is deposited on the floorand sidewall of high aspect ratio openings in the dual frequency reactorof FIG. 1. For this process, the metal target 18 of FIG. 1 is copper.The process gas is about 80% to 95% helium and about 5% to 10% hydrogen.The bias power is either an LF or HF frequency (or a combination ofboth) at a preferred level of about 20-40 Watts, or under 100 Watts. Thesource power is a VHF frequency of about 60 MHz, although superiorperformance may be achieved using a VHF source power frequency of 81MHz. Similarly, in all of the embodiments described above in thisspecification, the VHF source power frequency may be increased to 81 MHzto improve process performance. This may allow the VHF source powerlevel to be further increased in order to enhance process performancewithout increasing the ion energy.

PVD Reactor with ESC and Efficient VHF Radiator:

In the reactor of FIG. 19, the low efficiency and low power capacity ofthe electrostatic chuck as a VHF radiator is circumvented by integratingthe sputter target and rotating magnet in a highly efficient VHFradiator having high maximum VHF power capability.

Referring to FIG. 19 now, the reactor includes a vacuum chamber definedby a cylindrical side wall 10, a disk-shaped ceiling 12, and a wafersupport pedestal 14 for supporting a semiconductor wafer 16 to beprocessed. A target 18 of a metal (e.g., copper) to be deposited on thewafer 16 is mounted on the ceiling 12. A process kit consisting of acylindrical shield 20 surrounds the wafer 16 and the target 18. Arotating magnet (“magnetron”) 22 of the conventional type overlies thetarget 18 on the external side of the ceiling 12. A high voltage D.C.source 24 is coupled to the target 18 through a low-pass filter 25 thatincludes a series inductor 25 a and a shunt capacitor 25 b. A processgas injector 26 furnishes process gas from a supply 28 into the interiorof the chamber. A vacuum pump 30 maintains a desired sub-atmosphericpressure in the vacuum chamber.

The wafer pedestal 14 is coupled through an impedance match network 34to an HF or LF plasma bias power generator 38. The LF bias power appliedto the wafer determines the selectivity of the re-sputter/etch processfor horizontal surfaces. Plasma uniformity is enhanced by anelectromagnetic coil 43 wrapped around the cylindrical sidewall of thereactor chamber and supplied with D.C. current by a current sourcecontroller 45.

The wafer support pedestal 14 is an electrostatic chuck (ESC) of thetype illustrated in FIG. 2. Referring to FIG. 2, the wafer supportpedestal 14 of FIG. 19 consists of an insulating layer 50 mounted on aconductive base 51 and an electrode 52 such as a conductive mesh buriedinside the insulating layer 50. The pedestal structure can extenddownwardly in a coaxial arrangement consisting of a center conductor 54connected to the electrode 52, an insulating intermediate layer 56 andan outer conductor 58 connected to the conductive base 51. Theconductive base 51 can be coupled to the bottom of the cylindricalshield 20 by conductive tabs 60 to provide a more continuous groundreference. The center conductor 54 is coupled through an isolationcapacitor 76 to the RF match 34 while the outer conductor 58 isgrounded. The impedance match network 34 is coupled to the RF (HF or LF)plasma bias power generator 38. In addition, a D.C. chuck voltage source74 is connected to the wafer pedestal center conductor 54.

In FIG. 19, the magnetron 22 has a center axle 80 coupled to a centerarm 81 that is coupled to a magnet array 85. An electric motor (notshown) produces orbital motion by rotating the center axle 80.

FIG. 20 depicts an alternative embodiment, in which the rotating magnetor “magnetron” 22 has its center axle 80 coupled to the proximal end ofthe center arm 81, a dual planetary axle 82 connected to the distal endof the center arm 81 and to the proximal end of a planetary arm 83. Adual spin axle 84 is connected to the distal end of the planetary arm 83and a magnet array 85 that is spun around the axle 84. Planetary motionof the magnet array can be attained through a planetary gear arrangement(not shown).

In the preferred embodiment of FIG. 19, the magnets 85 a within themagnet array 85 may be permanent magnets arranged symmetrically in themanner of FIG. 21 so as to produce a toroidal confinement pattern of theions near the target 18, in accordance with the magnetic confinementpattern 85 b outlined in dashed line in FIG. 21. In one implementation,the target 18 was nineteen inches in diameter and the magnet array 85was five inches in diameter.

Referring again to FIG. 19, the metal (copper) sputter target 18 and themagnetron 22 are integrated in a highly efficient high power VHFradiator or applicator by providing a relatively thick (0.75 inchdiameter) RF rod 86 embedded in the metal target 18 and extendingaxially through a cylindrical hollow in the center axle 80 and throughthe ceiling 12. The RF rod 86 may be electrically insulated from thecenter axle 80. A VHF impedance match circuit 87 is coupled to (ormounted on) the external (top) end of the rod 86 and a VHF source powergenerator 88 is coupled to the match circuit 87. An output capacitor(not shown) of the RF impedance match 87 isolates the match 87 from D.C.current from the D.C. supply 24. Preferably, the VHF generator 88applies RF power at a frequency of about 81 MHz at a power level ofabout 3.5 kW (or more). In one implementation, the target 18 is copperand the RF rod 86 is a 0.75 inch diameter copper rod that is threadedinto the target 18. In any case, the copper rod 86 is relatively thick,being at least 0.50 inch in diameter or thicker (0.70 inch or more indiameter). FIG. 22 illustrates another embodiment in which plural RFrods 90 extend radially from the VHF impedance match circuit 87 to axialRF rods 91 that are coupled to the edge of the target 18. In theillustrated embodiment, the RF match circuit 87 is centered relative tothe disk-shaped metal target 18, the rods 90 are of a uniform length andthe rods 91 are of a uniform length. The RF rods 90, 91 are sufficientlythick (e.g., 0.70 inch in diameter) to provide highly efficient couplingof VHF power and withstand high VHF power levels (e.g., 3.5 kW andabove). In the embodiment of FIG. 22, there may be three sets ofsymmetrically arranged RF rods 90, 91 (as shown in the top view of FIG.23) or four sets of symmetrically arranged RF rods 90, 91 (as shown inthe top view of FIG. 24) or more. In the embodiments of FIGS. 1 and 19,the D.C. power from the source 24 applied to the metal (copper) target18 initially ionizes the carrier gas (e.g., helium), which starts thesputtering of the metal target 18. A relatively small fraction of themetal atoms sputtered from the target 18 are ionized in this process.Ions of the carrier gas (e.g., helium) produced by the D.C. power andsome copper ions are confined at the surface of the target 18 by thefield of the magnetron 22 in the toroidal confinement pattern discussedabove. The ionization fraction is insufficient for deposition on floorsof high aspect ratio openings on the wafer. In order to provide a veryhigh ionization fraction (e.g., in excess of 80%) that is capable ofsuch deposition, VHF power is employed to ionize the neutral metal atomssputtered from the target 18. For this purpose, in the embodiment ofFIG. 1, VHF power was coupled to the wafer to generate a VHF plasma nearthe wafer surface, which was possibly separate from the plasma generatedat the target 18 by the D.C. power applied to the target. In FIG. 1, themaximum VHF power level was severely limited by the fine geometry of themesh electrode of the ESC, thus limiting the maximum ionization fractionat the wafer to as low as 20% in some cases. We feel that an optimumionization fraction for deposition in high aspect ratio openings of a 65nm or 45 nm feature size is closer to or in excess of 80%. Therefore, inorder to overcome the limitation of the ESC, in the embodiment of FIG.19 the VHF power is applied to the target 18 through the thick RF rod86, as described above. The thickness of the metal target 18 and thethickness of the RF rod 86 is such that very high levels of VHF powermay be applied to the target 18 and, moreover, the target 18 is arelatively efficient VHF radiator. As a result, VHF power delivered tothe plasma may be nearly tripled, in some cases. The wafer-to-targetspacing can now be reduced, as the invention achieves a good level ofionization at a controllable deposition rate, without the need for alarge spacing.

In operation, the ionization fraction is no longer limited (e.g., below20% in some cases) by the low power threshold and efficiency of the ESC14, and instead very high levels of VHF power may be applied by the VHFgenerator 88. The resulting high ionization fraction (e.g., greater than80% in some cases) eliminates the need for very high D.C. power from thesupply 24 while enabling, for the first time, deposition of highlyconformal coatings in very high aspect ratio openings or vias.Preferably, the D.C. target power level is in a range of about 1000Watts to 2500 Watts. However, the deposition rate can be tightlycontrolled and set at very low levels by reducing the D.C. target powerfrom the supply 24 to very low levels (for example, 500 Watts or less),while using the VHF power boost the ionization fraction to the desiredlevel. This reduces the metal deposition rate sufficiently to eliminatethe need for a large wafer-to-target spacing. Heretofore, without theuse of VHF power, the high level of D.C. power required to attain thedesired ionization fraction produced uncontrollably high depositionrates unless the wafer-to-ceiling distance was increased to about 400 mm(to increase the deposition time to a mere 7 seconds). With VHF powerand D.C. power driving the target 18, the wafer-to-target spacing may bereduced to 50-70 mm or less (for example, for processing a 300 mmdiameter wafer). The result is that there is very little (or no)decrease in ionization fraction from the VHF-driven metal target 18 tothe wafer. In this way, the VHF plasma, generated by driving the(copper) target 18 with the VHF generator 88, is very close to thewafer, so that there is no need to apply VHF to the ESC 14 forsufficient ionization at the wafer. The D.C. power may be reduced asdesired without appreciably reducing ionization fraction, provided theVHF power is not reduced. Therefore, it is preferable to reduce or limitthe D.C. power to obtain a highly controllable deposition rate at thewafer, e.g., a deposition process that requires on the order of a minute(in contrast to the earlier techniques that afforded a depositionprocess time on the order of only seconds and which was thereforedifficult to control).

Application of HF power to the ESC 14 to generate an adequate rate ofre-sputtering of copper from horizontal surfaces or corners onto thehigh aspect ratio opening sidewalls has been discussed previously inthis specification. The HF power level required for this purpose issufficiently low so that the limitations of the ESC 14 (e.g., the finemesh electrode) do not limit the re-sputtering process. Therefore, theHF power for controlling re-sputtering is applied through the ESC 14 inthe reactor of FIG. 19.

An advantage of reducing the wafer-to-ceiling spacing is that thesurface area of the shield 20 is reduced, which reduces the amount ofsputtered metal (e.g., copper) that is wasted by depositing on theshield instead of the wafer. As a result, the metal target 18 and theshield 20 can be used to process a greater number of wafers (e.g.,20,000 wafer) before being replaced, thus reducing the per-wafer cost ofoperating the reactor. This represents an improvement of about an orderof magnitude.

Applying D.C. power and VHF power to the target 18 simultaneously whileapplying HF or LF power to the ESC 14 facilitates the independentsimultaneous control of three key parameters: deposition rate,ionization fraction and re-sputtering (re-flow) rate. The depositionrate is controlled by the level of D.C. power applied to the target 18by the D.C. supply 24. The ionization fraction is controlled by thelevel of VHF power applied to the target 18 by the VHF generator 88. There-sputter rate is controlled by the level of HF (or LF) power appliedto the ESC 14 by the HF (or LF) generator 38. In a preferred operatingmode, very low D.C. power (e.g., less than 500 Watts) is applied to thesputter target for a very low deposition rate, very high VHF power(e.g., over 3.5 kWatts) is applied to the sputter target for a highionization fraction sufficient for conformal coating in very high aspectratio openings, and a moderate level of HF power is applied to the ESC14 to provide an adequate rate of re-sputtering of deposited metal forre-deposition of metal on the sidewalls of high aspect ratio openings.The deposition rate may be increased if desired (by increasing thetarget D.C. power) up to a limit at which the flux of metal atomsthrough the VHF-generated plasma exceeds the ionization rate of whichthe plasma is capable, at which point the ionization fraction decreasessignificantly. Conversely, the VHF power may be decreased while applyinga given level of D.C. power to the target 18, until the same limit isreached at which the VHF-plasma density is overwhelmed by the flux ofmetal atoms from the target.

In one working example, the VHF power level was 3.5 kW. This induced arelatively small or negligible D.C. voltage on the target 18, so thatthe deposition rate is controlled almost entirely by the D.C. targetpower. The D.C. power applied to the target 18 in this example was 500Watts, the D.C. supply furnishing about 300 Volts and about 1.5 Amperes.

In one embodiment, the reactor of FIGS. 19 and 20 was employed forplasma enhanced physical vapor deposition of copper, the target 18 beingcopper. Helium gas was employed as the carrier gas to moderate there-sputter rate at the wafer, and hydrogen was included in the processgas (up to about 10% hydrogen) to prevent de-wetting of the depositedcopper on the sidewalls of high aspect ratio openings. The reactor ofFIGS. 19 and 20 may be used to deposit barrier layers (such as atantalum nitride barrier layer and/or a tantalum barrier layer). In sucha case, the target 18 is tantalum (or titanium or other suitable barriermetal). For a deposition of a tantalum nitride barrier layer, nitrogengas is introduced into the chamber.

As illustrated in FIG. 25, the metal sputtering target may be shaped asa truncated cone 18′ surrounding a flat circular ceiling 12 a. The RFrod 86 engages the target 18′ in a manner similar to that of FIG. 19,but is necessarily off-center because of the target shape. Analternative symmetrical or centered arrangement is suggested in dashedline, in which the VHF source 87, 88 is axially centered and feeds thetarget through multiple RF rods 86 that may be evenly spaced.

As illustrated in FIG. 26, the target 18 may be in registration with thecentered circular ceiling 12 a and surrounded by the truncated conicalceiling section 12′. One option (not illustrated in FIG. 26) is toprovide an inductive antenna over the truncated conical ceiling section12′ in the manner of FIG. 14.

As illustrated in FIG. 27, the metal sputtering target 18 may be shapedas an inverted bell or “U” shape, in the manner of FIG. 16. In oneimplementation, the RF rod 86 extends upwardly from the center of thetarget, as illustrated in solid line in FIG. 27. However, a preferredway may be to feed the VHF power at plural evenly spaced feed points 18a, 18 b along the periphery of the U-shaped target 18 of FIG. 27,through radial and axial RF rods 90′, 91′ as indicated in dashed line.

The flow diagram of FIG. 28 illustrates a method of performing physicalvapor deposition of copper onto an integrated circuit in a vacuumchamber of a plasma reactor, as follows: providing a copper target neara ceiling of the chamber (block 92 of FIG. 28), placing an integratedcircuit wafer on a wafer support pedestal facing the target near a floorof the chamber (block 93), introducing a carrier gas into the vacuumchamber (block 94), establishing a deposition rate on the wafer byapplying D.C. power to the copper target (block 95), establishing adesired plasma ionization fraction near the wafer by applying VHF powerto the copper target (block 96), promoting re-sputtering of copper onvertical surfaces on the wafer by coupling HF or LF power to the wafer(block 97), and maintaining a sufficiently small distance between thewafer and the target so that the VHF power control plasma ionizationfraction at the surface of the wafer (block 98).

A similar process may be employed using the reactor of FIG. 19 todeposit a barrier layer, such as tantalum and tantalum nitride barrierlayers, prior to copper deposition. For this purpose the target 18 istantalum. In order to deposit a tantalum nitride barrier layer, nitrogenis added to the process gas.

Arcing Suppression:

As discussed above, the ground strap 60 of FIG. 2 was introduced toprevent arcing at the shield 20. The shield is necessary to preventdeposition of material from the target 18 (Cu or Ta) on the chamberwalls. Arcing was not generally a problem for 200 mm diameter wafers.However, it was found that a PVD reactor for processing 300 mm waferstypically has significant arcing problems. The arcing arises from thelong RF return path that exists in the absence of the grounding strap60. This path is illustrated in dashed line in FIG. 1, and extends fromthe plasma to the interior surface of the shield 20 and down to thebottom of the shield 20, then up the outer surface of the shield 20 tothe side wall 10, down the interior surface of the sidewall 10 andthence to the outer coaxial shield. This latter portion of the path isbest viewed in FIG. 2 and is indicated in dashed line as extending alongthe ESC base 51 to the coaxial shield 58. This conductive path is solong that successive voltage peaks and nodes will occur along the pathat intervals determined by the frequency of the applied RF power,leading to arcing or ignition of extraneous plasma below the pedestal oroutside the shield 20. These effects will cause contamination of theprocess and uncontrolled diversion of RF power from the process.Although introduction of the conductive grounding strap 60 (FIG. 2)solves the problems of arcing and extraneous plasma ignition, itrequires the placement of a number of such straps at intervals along theapplied periphery that are less than the wavelength of the applied RFpower. For example, three straps 60 placed at 120 degree intervals alongthe shield periphery may suffice where the applied RF frequency is 13.56MHz. However, such an array of grounding straps would block access ofthe wafer to the ESC 14. Therefore, such grounding straps cannot beplaced at uniform intervals along the shield periphery, thereby makingit difficult to prevent arcing or extraneous plasma ignition.

FIGS. 29A, 29B and 29C are elevational, perspective and top views, of aphysical vapor deposition reactor similar to that of FIG. 19 butincorporating an array of compressible grounding tabs 224 of the typedepicted in FIGS. 18A and 18B. The perspective view of FIG. 29B depictsthe reactor with the ESC in a retracted position at which thecompressible tabs 224 are not contacting the shield 20. As shown in thetop view of FIG. 29C, for an 81 MHz applied RF frequency, as many aseight compressible conductive tabs 224 a-224 g are deployed at uniformintervals D around the periphery of the ESC 14, each of the tabs 224being mounted on the metal flange 226 extending from the ESC base 51.For lower RF frequencies or longer wavelengths, the interval D may belarger, requiring only three tabs 224, as illustrated in the top view ofFIG. 29D. The tab-to-tab interval D must be less than the wavelength ofthe RF power applied by the VHF generator 88 so that the spacing betweengrounded (zero RF voltage) points prevents formation of resonances orvoltage peaks along the shield 20. This interval may need to besubstantially less than the free space wavelength at the applied RFfrequency because the plasma in the chamber reduces the effectivewavelength along the interior surface of the conductive shield 20. Thecompressible conductive tabs 224 remain below the plane of the wafer 16when the ESC 14 is retracted, so that there is full access for the waferto the ESC 14 while the tabs 224 may be placed at uniform intervals tooptimize suppression of arcing and of extraneous plasma ignition.

While the invention has been described in detail with reference topreferred embodiments, it is understood that variations andmodifications thereof may be made without departing from the true spiritand scope of the invention.

1. A physical vapor deposition reactor, comprising: a vacuum chamberincluding a sidewall, a ceiling and a retractable wafer support pedestalnear a floor of the chamber, and a vacuum pump coupled to the chamber,said retractable wafer support pedestal having an internal electrode anda grounded base with a conductive annular flange extending from saidbase; a process gas inlet coupled to said chamber and a process gassource coupled to said process gas inlet; a metal sputter target at saidceiling; a high voltage D.C. source coupled to said sputter target; anRF plasma source power generator coupled to said metal sputter targetand having a frequency suitable for exciting kinetic electrons; and aremovable shield protecting said sidewall and plural compressibleconductive tabs dispersed at generally uniform intervals on said annularflange and engaging a bottom edge of said shield whenever saidretractable wafer support pedestal is in an unretracted position, eachof said uniform intervals being less than a wavelength corresponding tothe frequency of said RF plasma source power generator.
 2. The reactorof claim 1 wherein said wafer support pedestal comprises anelectrostatic chuck.
 3. The reactor of claim 1 further comprising an RFplasma bias power generator coupled to said internal electrode of saidretractable wafer support pedestal and having a frequency suitable forcoupling energy to plasma ions.
 4. The reactor of claim 1 furthercomprising a solid metal RF feed rod having a diameter in excess ofabout 0.5 inches engaging said metal sputter target, said RF feed rodextending axially above said target through said ceiling and beingcoupled to said RF plasma source power generator.
 5. The reactor ofclaim 4 further comprising an RF match circuit coupled between said RFplasma source power generator and said RF feed rod, said RF matchcircuit being mounted on said RF feed rod.
 6. The reactor of claim 4further comprising a magnet array overlying said ceiling and a centeraxle about which said magnet array is rotatable, said center axle havingan axially cylindrical hollow passageway therethrough, said metal rodextending through said passageway.
 7. The reactor of claim 6 furthercomprising planetary motion apparatus coupled between said magnet arrayand said center axle, said magnet array comprising an array of magneticpoles arranged to produce a generally toroidal-shaped confinementpattern of ions near said target.
 8. The reactor of claim 1 wherein saidwafer support and said target are separated by a distance which does notexceed about one fourth of the diameter of said wafer support.
 9. Thereactor of claim 1 further comprising a removable shield surrounding aprocessing zone encompassing the wafer support pedestal and separatingsaid processing zone from the sidewall of the chamber.
 10. The reactorof claim 1 wherein said metal sputter target comprises copper.
 11. Thereactor of claim 1 wherein said metal sputter target comprises tantalum.12. A physical vapor deposition and re-sputter plasma reactor,comprising: a vacuum chamber including a sidewall, a ceiling and aretractable wafer support pedestal near a floor of the chamber, and avacuum pump coupled to the chamber, said pedestal having an internalelectrode and a grounded base with a conductive annular flange extendingfrom said base; a metal sputter target at said ceiling and a highvoltage D.C. source coupled to said sputter target and capable ofexciting a target-sputtering plasma near said target; an RF plasmasource power generator coupled to said wafer support pedestal and havinga frequency suitable for exciting kinetic electrons; an RF plasma biaspower generator coupled to said internal electrode and having afrequency suitable for accelerating ions from said wafer-sputteringplasma across a plasma sheath near said wafer support pedestal; and aremovable shield protecting said sidewall and plural compressibleconductive tabs dispersed at generally uniform intervals on said annularflange and engaging a bottom edge of said shield whenever saidretractable wafer support pedestal is in an unretracted position, eachof said uniform intervals being less than a wavelength corresponding tothe frequency of said RF plasma source power generator.
 13. Theapparatus of claim 12 further comprising a magnetron overlying saidtarget for confining enhancing said target-sputtering plasma.
 14. Theapparatus of claim 12 wherein the frequency of said source powergenerator is a VHF frequency and the frequency of said bias powergenerator is an HF or LF frequency.
 15. The apparatus of claim 14wherein said bias power generator is set to a power level sufficient todirect ions of said wafer-sputtering plasma to sputter horizontalsurfaces on a wafer mounted on said wafer support pedestal and avoidsputtering vertical surfaces on said wafer.
 16. The apparatus of claim14 wherein said target comprises tantalum and said process gas comprisesnitrogen.
 17. The apparatus of claim 12 further comprising a high passfilter coupled between said source power generator and said waferpedestal and a low pass filter coupled between said bias power generatorand said wafer support pedestal.
 18. The apparatus of claim 12 whereinsaid RF plasma source power generator and said RF plasma bias powergenerator have respectively adjustable RF power levels for independentcontrol of conformality of the deposited layer to the vias, and ofselectivity of the deposited layer for horizontal and for verticalsurfaces of the via.
 19. The apparatus of claim 18 further comprising aprocess power controller coupled to power level control inputs of saidD.C. source, said RF plasma source power generator and said RF plasmabias power generator, said process controller being configurable into atleast two of three states comprising: (a) a conformal deposition statecomprising a low power level of D.C. source, a high power level of RFplasma source power generator and a low power level of said RF plasmabias power generator; (b) a non-conformal deposition state comprising alow power level of D.C. source, a high power level of said RF plasmasource power generator, and an at least nearly zero power level of saidRF plasma bias power generator; and (c) a punch through re-sputter statecomprising a low power level of said D.C. source, a high power level ofsaid RF plasma source power generator, and a high power level of said RFplasma bias power generator.
 20. The apparatus of claim 12 furthercomprising an electromagnet coil around said chamber and a D.C. currentsource coupled to said coil.